Light-stable colored transparent composite films

ABSTRACT

Composite film structures exhibit a predetermined finished color tone comprised of a transparent film layer which exhibits a color deficiency as compared to the finished color tone, and a pigment which is visually associated with, and satisfies the color deficiency of, the film layer. Most preferably, the pigment is provided as a homogenous dispersion in a transparent color-matching layer positioned adjacent to the film layer. Thus, when the film and color-matching layers are viewed collectively as a unit, the perceived color tone will be that of the finished predetermined color tone. That is, the color-matching layer provides visually an additive effect on the perceived color of the composite film structure.

FIELD OF THE INVENTION

[0001] The present invention relates to colored transparent films. Inparticularly preferred forms, the present invention is embodied incolored transparent composite films which exhibit exceptional lightstability (anti-fading) characteristics.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] Transparent colored films are employed in a number of end-useapplications, for example, as window films, light filters and the like.When employed as window films in the building and automotive industries,the colored transparent window films are typically adhered to glasswindow surfaces via a suitable adhesive so as to reduce the amount ofnear infrared, ultra-violet and/or visible radiation entering thebuilding or automotive interior space. Such solar films therefore assistthe occupants by providing less glare, reducing interior heating effectsand the like.

[0003] Colored transparent films are typically provided by dyeing asuitable thermoplastic (preferably polyester) film substrate as isdisclosed more completely in U.S. Pat. Nos. 3,989,453; 3,943,105;3,932,126; 4,050,892 and 4,047,889 (the entire content of each beingincorporated expressly hereinto by reference). Thus, the thermoplasticfilm substrate may be preconditioned to enhance affinity to solvent ordisperse dyes, followed by contacting the preconditioned film substratewith an organic dye-containing paste or solution.

[0004] Gray-toned (i.e., so-called “smoke-colored”) transparent filmsare especially desirable in the market and are produced by suitabledyeing of the film substrates using the necessary proportions of red,blue and yellow organic dyes. One problem which these conventionalgray-toned transparent films experience, however, is that the yellow dyecomponent is more susceptible to light degradation as compared to thered and blue dye components. Thus, over prolonged exposure to light, theyellow dye component of the gray-toned dyed film tends to decompose(fade) thereby changing the visual appearance of the film undesirably toa more purple color tone due to the then more dominant presence of thered and blue dyes remaining in the dyed film.

[0005] It would therefore be especially desirable if colored (dyed)transparent thermoplastic films could be rendered more light stablethereby minimizing (or preventing entirely) fading and/or changing colortones over time. It is towards fulfilling such a need that the presentinvention is directed.

[0006] Broadly, the present invention is embodied in composite filmstructures exhibiting a predetermined finished color tone comprised of atransparent film layer which exhibits a color deficiency as compared tothe finished color tone, and a pigment which is visually associatedwith, and satisfies the color deficiency of, the film layer. Mostpreferably, the pigment is provided as a homogenous dispersion in atransparent color-matching layer positioned adjacent to the film layer.Thus, when the film and color-matching layers are viewed collectively asa unit, the perceived color tone will be that of the finishedpredetermined color tone. In other words, the color-matching layerprovides visually an additive effect on the perceived color of thecomposite film structure.

[0007] As a practical matter, therefore, the color deficiency of thefilm layer can be selected to be that particular dye which is more lightunstable and thereby more likely to degrade over time when exposed tolight. The pigment in the color-matching layer (which would inherentlybe more color stable as compared to the dye) may then be selected tosatisfy the color deficiency in the film layer. As a result, a morelight stable transparent color film composite structure ensues (i.e.,due to the lesser amount (if any) of more light unstable dye(s) in thefilm and the greater amount of more light stable pigments in theadjacent color-matching layer).

[0008] These and other aspects and advantages of the present inventionwill become more clear after careful consideration is given to thefollowing detailed description of the preferred exemplary embodiments.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0009] The file of this patent contains at least one drawing executed incolor. Copies of this patent with color drawing(s) will be provided bythe Patent and Trademark Office upon request and payment of thenecessary fee.

[0010] Reference will hereinafter be made to the accompanying drawings,wherein like reference numerals throughout the various FIGURES denotelike elements, and wherein,

[0011]FIG. 1 is a greatly enlarged schematic cross-section of oneembodiment of a composite film in accordance with the present invention;

[0012]FIG. 2 is a greatly enlarged schematic cross-section of thecomposite film depicted in FIG. 1 applied onto a glass substrate;

[0013]FIG. 3 is a greatly enlarged schematic cross-section of anotherembodiment of a composite film in accordance with the present invention;

[0014]FIG. 4 is a greatly enlarged schematic cross-section of yetanother embodiment of a composite film in accordance with the presentinvention;

[0015] FIGS. 5-9 are graphical representations of the color stabilitytest data obtained by the Example 2 below; and

[0016] FIGS. 10-13 are color photoprints each visually depicting thenon-weathered finished color tone (visible on left-hand side of eachsample) and the results of accelerated weather testing (visible on theright-hand side of each sample) on such finished color tone obtainedaccording to Example 2 below, wherein FIG. 10 is a sample in accordancewith the present invention, and FIGS. 11-13 are each representative ofcommercially available transparent colored films.

DETAILED DESCRIPTION OF THE INVENTION

[0017] I. Definitions

[0018] The terms “hue”, “chroma” (sometimes referred to in the art asintensity of color saturation) and “value” are the color coordinatesassociated with the Munsell color system (see U.S. Pat. No. 824,374, theentire content of which is incorporated fully hereinto by reference).

[0019] The term “colorant” is any material which exhibits hue, chromaand/or value. Thus, a colorant may be one which exhibits a perceivedcolor (e.g. red, blue and/or yellow) in which case it has a definite hueand/or chroma and is characterized as being chromatic. A colorant mayalso be a material which lacks both hue and chroma, but whichnonetheless contributes to the value coordinate, in which case it ischaracterized as achromatic.

[0020] A “pigment” is a particulate material which is a colorant.

[0021] The term “transparent” connotes the ability to perceive visuallyan object, indicia, words and the like through a medium, which is a filmin the preferred embodiment of this invention. More specifically, theterm “transparent” as used herein and in the accompanying claims meansthe medium (e.g., film) exhibits a haze value (ASTM D 1003-61) of notgreater than about 25%, preferably not greater than about 5%, and avisible light transmission (VLT) through the film structure (ASTM E903and NFRC 300-93, “Procedure for Determining the Solar Optical Propertiesfor Simple Fenestration Products”) of between about 1% to about 90%,preferably between about 5% to about 80%, and most preferably betweenabout 5% to about 50%. The particular haze value and VLT of a filmstructure will thus depend on its intended end use application. Forexample, window films for use with automotive glass will typically havea relatively low have value (e.g., not greater than 5%) and a relativelyhigh VLT (e.g., between about 5 to about 50%). Film structures intendedfor shade applications, however, can tolerate relatively greater hazevalues and relatively lower VLT as compared to automotive window films.

[0022] II. Detailed Description of the Preferred Embodiments

[0023] Accompanying FIG. 1 shows an enlarged schematic cross-section ofone embodiment of a composite film 10 having a finished color tone inaccordance with the present invention. Specifically, the composite film10 necessarily includes a film layer 12 and a color-matching layer 14.The film layer 12 is formed of a suitable thermoplastic, preferably apolyester, such as polyethylene terephthalate (PET), or other suitablethermoplastics, such as, for example, polyacrylic, polyimides,polyamides (e.g., nylons), and polyolefins (e.g., polypropylenes,polyethylenes and the like). The thermoplastic films employed in thepractice of this invention can include conventional additives eithercoated upon, or homogeneously blended within, the film. Thus, thethermoplastic films may include UV-absorbers, stabilizers, fillers,lubricants and other processing aids, and the like.

[0024] The thickness of film layer 12 is most advantageously betweenabout 0.25 mil to 14 mils. For example, when composite film 10 isemployed as a solar film for windows, the thickness of film layer 12 istypically in the range between about 0.5 to about 1.0 mil. When thecomposite film 10 is employed for other applications, such as a sunshade, the thickness of film layer 12 may be between about 1.0 mil toabout 3.0 mils.

[0025] The film layer 12 may be uncolored or colored. If uncolored, thenthe film layer 12 will exhibit a complete deficiency in all three colorcoordinates of hue, chroma and value. If colored, then the film layer 12will exhibit a deficiency in a least one color coordinate of hue, chromaand value as compared to the finished color tone of the composite film10. In either the uncolored or colored case, therefore, the film layer12 will exhibit a deficiency in at least one of hue, chroma and value ascompared to the finished color tone of the composite film 10.

[0026] The color deficiency of the film layer 12 is satisfied in thecolor-matching layer 14. Specifically, the color matching layer 14includes a homogeneous dispersion of pigment therein which satisfies thecolor deficiency in the film layer 12. As a result, when the film andcolor-matching layers 12, 14 are viewed collectively, the additiveeffect of their respective color tones will result in a visualperception corresponding to the finished color tone of the compositefilm 10. Most preferably, the color-matching layer is interior of thefilm layer 12 (i.e., positioned closer to the sunlight than the filmlayer 12).

[0027] In the composite film 10 shown in FIG. 1, the color-matchinglayer 14 is most preferably formed by dispersing the pigment throughouta mounting adhesive. Virtually any suitable pressure or non-pressuresensitive mounting adhesive may be employed in the practice of thepresent invention which allows the composite film 10 to be adheredsecurely to a desired support substrate. In this regard, the preferredmounting adhesive is an acrylic pressure sensitive adhesive commerciallyavailable from Solutia, Inc. under the tradename GELVA® 263 adhesivewhich is supplied as an acrylic resin solution.

[0028] The pigment that is employed in the practice of the presentinvention is broadly characterized as a particulate colorant material.That is, the pigment will impart a desired color tone to thecolor-matching layer and is selected based on its color characteristicsof hue, chroma and/or value as well as its average particle sizeproperties. Thus, the pigment employed in the present invention can beeither chromatic in that is has at least one of hue and chromacharacteristics, or can be achromatic in which case it is lacking inboth hue and chroma characteristics but has a value characteristic. Thepigment also cannot have too large a particle size as this wouldadversely scatter light making the composite film less transparent(i.e., more hazy, translucent or opaque). Therefore, the pigmentemployed in the practice of the present invention is required to have anaverage particle size of less than about 0.50 μm, more preferably lessthan about 0.10 μm, and most preferably less than about 0.05 μm.

[0029] Virtually any pigment that satisfies the above-noted criteria maybe employed in the practice of this invention. Thus, pigments based oniron oxide, lead, chrome, ultramarine, iron blue, cadmium and the likemay be employed. For example, when the color deficiency in the filmlayer 12 is with respect to the yellow hue and/or chroma, then aparticularly preferred pigment is red iron oxide (which actually visiblyhas a yellowish color tone).

[0030] When employed as a dispersion within the mounting adhesive, thepigments employed in the practice of the present invention mayconveniently be mixed with the adhesive so as to be homogeneouslydispersed therein and then applied onto the film layer 12 as thecolor-matching layer 14 in any known manner, such as dipping, spraying,padding, roller coating, gravure coating, printing or the like.Following application, the color-matching layer 14 (i.e., the adhesivematerial containing a homogenous dispersion of pigment therein) may becovered by a suitable release layer 18 to allow the composite film 10 tobe handled and shipped prior to being mounted onto a substrate. In thisregard, just prior to use, the release layer 18 will be removed orpeeled away from the adhesive (color-matching) layer 14 thereby leavingthe remaining laminated components of the composite film (noted byreference numeral 10′ in FIG. 2). The composite film components 10′ maythen be affixed to a substrate, for example, a glass substrate (e.g., abuilding or automotive window) 20 as shown in FIG. 2.

[0031] One particularly preferred embodiment of the present invention isa gray-toned composite film having a film layer 12 which is colored withpredominantly red and blue dyes and thus will exhibit a yellow colordeficiency (i.e., will exhibit a purple-like color tone). Thus, thepreferred gray-toned composite may be dyed with a minor, butinsufficient, amount (if any) of a yellow dye. The color-matching layer14 will thus be formed of a mounting adhesive in which a yellow-coloredpigment (e.g., an iron oxide) is dispersed homogeneously. Thus, theyellow-colored pigment in the color-matching layer 14 will satisfy theyellow color deficiency of the dyed film layer 12.

[0032] The composite film 10 may also include an exterior (i.e.,relative to the rigid substrate, typically glass, on which the film isadhered) polymeric protective coating 16 (typically called a “hardcoat”in art parlance). The protective coating 16 serves to impart abrasionresistance, scratch and/or chemical resistance to the composite film 10or 10′. Typically, such coatings are curable either thermally or byradiation and can be, for example, highly cross-linked acrylic acidesters. Particularly preferred materials that may be employed in theprotective coating 16 are the radiation polymerizable acrylic coatingsdisclosed more fully in U.S. Pat. No. 4,557,980 (the entire content ofwhich is expressly incorporated hereinto by reference). If present, theprotective coating 16 will typically have a thickness of less than 10 μ,and preferably between about 1 μ to about 4.5 μ.

[0033] Although the composite film 10 has been described wherein thepigment is dispersed throughout an adhesive material so as to form thecolor-matching layer 14, it may be desirable to disperse some (or all)of the pigment in the protective coating 16, in which case both thelayers 14 and 16 (or just the layer 16) constitute the color-matchinglayer to satisfy the color deficiency of the film layer 12. Furthermore,it is possible that the pigment could be dispersed throughout, and thusbe integrally provided with, the film layer 12. The film layer 12 withits integral dispersion of pigment could then be dyed to have a colordeficiency which is integrally satisfied by the pigment containedtherewithin.

[0034] Accompanying FIG. 3 shows another embodiment of a composite film30 according to the present invention. In this regard, like thecomposite film 10 discussed above, the composite film 30 includes athermoplastic (preferably PET) film layer 12, a color-matching adhesivelayer 14 containing a pigment dispersed therein, a protective exteriorcoating 16, and a release layer 18 covering the adhesive color-matchinglayer 14. However, according to the embodiment depicted in FIG. 3, thecomposite film 30 is provided with another film layer 32 which isadhered to the film layer 12 by a suitable laminating adhesive layer 34.

[0035] The film layer 32, like the film layer 12 may be uncolored orcolored as may be desired. Furthermore, the film layer 32 may bemetallized. That is, the film layer 32 may be provided with a relativelythin metal coating, e.g., aluminum, nickel alloys (e.g., nickel-chromiumalloys or their oxides), silver, titanium and the like, applied byconventional vacuum deposition techniques. If present, the metallizedlayer will typically have a thickness of between about 50 Å to about 600Å.

[0036] The pigment in the adhesive color-matching layer 14 mayalternatively, or additionally, be provided in the laminating adhesivelayer 34, if desired. Thus, the pigment may be distributed among thelayers 16, 14 and 32, or be contained in any one of such layers as maybe desired. For example, as shown in FIG. 4, a laminated composite film40 is provided with thermoplastic film layers 42 and 44 laminated to oneanother with a suitable adhesive layer 46. One or both of the filmlayers 42, 44 may thus be dyed in a manner which provides for a colordeficiency as compared to the finished color tone of the composite film40. A pigment satisfying the criteria noted previously may thus bedispersed homogeneously throughout the adhesive layer 46 so as tosatisfy the color deficiency of the film layers 42 and/or 44. Thecomposite film 40 depicted in FIG. 4 is thus suitable as a window shadefilm.

[0037] The transparent films according to the present invention can be“engineered” to provide desired light transmission characteristics,depending on the end-use application. Most preferably, the coloredtransparent composite films will have a visible light transmission (VLT)of between about 1% to about 90%, preferably between about 5% to about80%, and most preferably between about 5% to about 50%. The transparentfilms of this invention will also most preferably exhibit haze values ofnot greater than about 25%, preferably not greater than about 5%.

III. EXAMPLES

[0038] The present invention will be further understood afterconsideration is given to the following non-limiting Examples.

Example 1

[0039] A red iron oxide (Cl R101) pigment was blended with ascratch-resistant methyl methacrylate hardcoat material (U.S. Pat. No.4,557,980) using methyl iso-butyl ketone (MIBK) solvent in an amount of1 wt. % iron oxide in the hardcoat plus MIBK. The resulting mixture hadCIE lab values (10⁰ standard observer and D65 light source) ofL*=94.18/a*=0.84/b*=9.25 and was applied at a thickness of 1.0-1.5microns using standard gravure coating methods onto a dyed polyesterfilm so as to achieve a gray color tone. CIE Lab values (100 observerwith D65 light source) for the resulting coated film were:L*=81.13/a*=−3.96/b*=4.9. The coated film was mounted on clear, singlestrength glass using an acrylic pressure sensitive adhesive (GELVA® 263adhesive, Solutia, Inc.) which contained a benzophenone UV-absorber. Thefilm and glass structure was then subjected to accelerated Xenon weathertesting according to ASTM G26-93. The film showed enhanced colorstability characteristics after 1200 hours exposure to the Xenon weathertesting conditions.

Example 2

[0040] A red iron oxide (Cl R101) pigment was blended in an amount of 1wt. % with an acrylic pressure sensitive adhesive (GELVA® 263 adhesive,Solutia, Inc.) which contained a benzophenone UV-absorber. The resultingblend of red iron oxide pigment and adhesive was used to mount the samedyed gray-tone polyester film employed in Example 1 to a clear, singlestrength glass for weather testing according to ASTM G26-93.

[0041] The results of the weather testing on the composite film inaccordance with the present invention were compared to the weathertesting results of three dyed polyester film products commerciallyavailable from CPFilms, Inc. of Martinsville, Va., identified by AT 35Gr SR HPR (Comp. 1), AT 35 Ch SR HPR (Comp 2) and AT 35 Bz SR PS (Comp3). The results of such comparative testing are shown graphically in theaccompanying FIGS. 5-9. In addition, the results of the acceleratedweather testing are shown photographically in accompanying FIGS. 10-13.In this regard, the left-hand side of each of FIGS. 10-13 represents thefinished color tone of the film unexposed to the weather testingconditions, whereas the right-hand side of FIGS. 10-13 was exposed to,and thus depict the condition of the film after, weather testing. As isevident, the composite film in accordance with the invention (FIG. 10)shows enhanced color stability characteristics as compared to theconventional films Comp. 1 (FIG. 11), Comp. 2 (FIG. 12) and Comp. 3(FIG. 13).

Example 3

[0042] Example 2 was repeated except that the 1 wt. % iron oxidecontaining adhesive was used to laminate a metallized film (1 mil thickaluminum metallized layer on a 15% visible light transmission gray-toneddyed polyester film) to a 0.5 mil thick clear polyester film containingUV absorbers. The resulting laminated composite film structure wasmounted to a single strength glass using a non-pigmented acrylicpressure sensitive adhesive (GELVA® 263 adhesive, Solutia, Inc.) whichcontained a benzophenone UV-absorber. Following weather testing, thesample was visually observed for corrosion and coating instability withno significant anomalies being detected.

[0043] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A transparent film which exhibits a predeterminedfinished color tone comprising: a transparent film layer which exhibitsa color deficiency in at least one of hue, chroma and value as comparedto the predetermined finished color tone; and at least one pigmentvisually associated with the film layer and exhibiting a matching colortone satisfying the color deficiency of said film layer to therebyimpart to the composite film the predetermined finished color tone whenthe film and at least one pigment are viewed collectively as a unit. 2.The transparent film of claim 1, wherein said at least one pigment isdispersed throughout a transparent color-matching layer adjacent saidfilm layer.
 3. The transparent film of claim 1, wherein said film layeris a thermoplastic.
 4. The transparent film of claim 3, wherein saidthermoplastic film layer is polyethylene terephthalate.
 5. Thetransparent film of claim 1, wherein said at least one pigment ishomogeneously dispersed as a blend throughout the transparent filmlayer.
 6. The transparent film of claim 2, wherein the film layer has ayellow color deficiency, and wherein the color-matching layer includes adispersion of a yellow-colored pigment.
 7. The transparent film of claim6, wherein the pigment is an iron oxide.
 8. The transparent film ofclaim 1, further comprising a protective coating layer on the filmlayer.
 9. The transparent film of claim 1, wherein said film layerincludes first and second film layers laminated to one another.
 10. Thetransparent film of claim 9, further comprising a protective coatinglayer of the film layer.
 11. The transparent film of claim 1, whereinsaid film layer includes a metallized layer.
 12. The transparent film ofclaim 1, wherein said pigment has an average particle size of less thanabout 0.50 μm.
 13. The transparent film of claim 1, wherein the pigmenthas have an average particle size of less than about 0.10 μm.
 14. Thetransparent film of claim 1, wherein the pigment has have an averageparticle size of less than about 0.05 μm.
 15. The combination comprisedof a glass substrate, and affixed thereto, a transparent film accordingto claim
 1. 16. A transparent composite film having a finished graycolor tone comprising: a transparent polyester terephthalate film layerwhich is dyed to exhibit a selected color tone having a color deficiencyin at least one of red, blue and yellow color tones as compared to thefinished gray color tone of the composite film; and a transparentcolor-matching layer adjacent said film layer containing a pigment whichexhibits a matching color tone satisfying the color tone deficiency ofsaid film layer.
 17. The transparent composite film of claim 16, whereinsaid film layer exhibits a yellow color deficiency, and wherein saidpigment has a yellow color tone which satisfies the yellow colordeficiency of the film layer.
 18. The transparent composite film ofclaim 16, wherein the color-matching layer is comprised of an adhesivewith the pigment dispersed homogeneously throughout the adhesive. 19.The transparent composite film of claim 18, further comprising aprotective coating adjacent to the film layer on a side opposite to thecolor matching layer.
 20. The transparent composite film of claim 16,wherein the color-matching layer is a protective polymeric layeradjacent to the film layer with the pigment dispersed homogeneouslythroughout the protective polymeric layer.
 21. The transparent compositefilm of claim 16, wherein the film layer includes first and secondthermoplastic film layers, and an adhesive laminating layer positionedbetween and laminating the first and second thermoplastic film layers toone another.
 22. The transparent composite film of claim 21, wherein theadhesive layer comprises said color-matching layer such that saidpigment is dispersed homogeneously throughout said adhesive layer. 23.The transparent film of claim 16, wherein said pigment has an averageparticle size of less than about 0.50 μm.
 24. The transparent film ofclaim 16, wherein the pigment has have an average particle size of lessthan about 0.10 μm.
 25. The transparent film of claim 16, wherein thepigment has have an average particle size of less than about 0.05 μm.26. The combination comprising a glass substrate, and affixed thereto, atransparent composite film according to claims
 16. 27. A process formaking a transparent film which exhibits a predetermined finished colortone comprising the steps of: (a) providing a transparent film layerwhich exhibits a color deficiency in at least one of hue, chroma andvalue as compared to the predetermined finished color tone; and (b)visually associating with said film layer at least one pigmentexhibiting a matching color tone satisfying the color deficiency of saidfilm layer and thereby imparting to the composite film the predeterminedfinished color tone when the film and color-matching layers are viewedcollectively as a unit.
 28. The process of claim 27, wherein step (b)includes dispersing the pigment homogeneously throughout an adhesive toform an adhesive pigment dispersion, and then forming a layer of theadhesive pigment dispersion adjacent to the film layer.
 29. The processof claim 27, wherein step (b) includes dispersing the pigmenthomogeneously throughout a curable polymeric coating material to form acoating pigment dispersion, forming a layer of the curable coatingpigment dispersion adjacent to the film layer, and curing the coatingpigment dispersion to form a protective hard coating thereon.
 30. Theprocess of claim 27, wherein step (a) includes providing first andsecond film layers, and laminating said first and second film layers toone another with a laminating adhesive, and wherein step (b) includesdispersing the pigment homogeneously throughout the laminating adhesiveto form a laminating adhesive pigment dispersion.
 31. The process ofclaim 27, wherein step (b) includes dispersing the pigment throughoutthe film layer.
 32. The process of claim 27, wherein the pigment has anaverage particle size of less than about 0.50 μm.
 33. The transparentfilm of claim 27, wherein the pigment has have an average particle sizeof less than about 0.10 μm.
 34. The process of claim 27, wherein thepigment has an average particle size of less than about 0.05 μm.